The impact of infection on host competition and its relationship to parasite persistence in a Daphnia microparasite system

Evolutionary studies often estimate fitness components with the aim to make predictions about the outcome of selection. Depending on the system and the question, different fitness components are used, but their usefulness for predicting the outcome of selection is rarely tested. Here we estimate host fitness components in different ways with the aim to test how well they agree with each other and how well they predict host fitness at the population level in the presence of the parasite. We use a Daphnia magna-microparasite system to study the competitive ability of host clones in the absence and presence of the parasite, the infection intensity of the parasite in individuals of twelve host clones (an estimate of both host resistance and parasite reproductive success), and parasite persistence in small host populations (an estimate of R 0 of the parasite). Analysis of host competitive ability and parasite persistence reveals strong host genotype effects, while none are found for infection intensity. Host competitive ability further shows a genotype-specific change upon infection, which is correlated with the relative persistence of the parasite in the competing hosts. Hosts in which the parasite persists better suffer a competitive disadvantage in the parasite's presence. This suggests that in this system, parasite-mediated selection can be predicted by parasite persistence, but not by parasite infection intensit

Lab life : when your PhD (almost) falls apart

As a chance observation threatens to unravel several years of work, a PhD student must choose what to do next

Production de spiruline à la ferme : produire de la spiruline à la ferme grâce au digestat et à la chaleur excédentaire d’une installation de biogaz

The development of projects coupling an agricultural anaerobic digestion installation with the production of spirulina is an attractive concept, since the waste streams from the methanisation and from biogas valorization can be used to produce a high value product. This principle allows a better energetic valorization of surplus heat and of exhaust gases coming from the cogeneration unit. The limits of this configuration have been evaluated for Switzerland to study if the implementation of such coupling increases the competitiveness of agricultural anaerobic digestion. The thermal autonomy of the plant has been established as the main criterion to design the spirulina production units. For different working conditions (light radiation, nutrients source, size of methanisation units), the potential production of spirulina has been evaluated. The process energy yield, the environmental impact and the process economy show that 50% of surplus heat can be valorized, being 85-90% of heat contained in the exhaust gases; that the decrease in carbon dioxide emissions is not relevant and that, for the conditions tested, the operating costs are currently too high to allow the economic feasibility of the project

Cytological and molecular description of Hamiltosporidium tvaerminnensis gen. et sp. nov., a microsporidian parasite of Daphnia magna, and establishment of Hamiltosporidium magnivora comb. nov

We describe the new microsporidium Hamiltosporidium tvaerminnensis gen. et sp. nov. with an emphasis on its ultrastructural characteristics and phylogenetic position as inferred from the sequence data of SSU rDNA, alpha- and beta-tubulin. This parasite was previously identified as Octosporea bayeri Jírovec, 1936 and has become a model system to study the ecology, epidemiology, evolution and genomics of microsporidia - host interactions. Here, we present evidence that shows its differences from O. bayeri. Hamiltosporidium tvaerminnensis exclusively infects the adipose tissue, the ovaries and the hypodermis of Daphnia magna and is found only in host populations located in coastal rock pool populations in Finland and Sweden. Merogonial stages of H. tvaerminnensis have isolated nuclei; merozoites are formed by binary fission or by the cleaving of a plasmodium with a small number of nuclei. A sporogonial plasmodium with isolated nuclei yields 8 sporoblasts. Elongated spores are generated by the most finger-like plasmodia. The mature spores are polymorphic in shape and size. Most spores are pyriform (4·9-5·6×2·2-2·3 μm) and have their polar filament arranged in 12-13 coils. A second, elongated spore type (6·8-12·0×1·6-2·1 μm) is rod-shaped with blunt ends and measures 6·8-12·0×1·6-2·1 μm. The envelope of the sporophorous vesicle is thin and fragile, formed at the beginning of the sporogony. Cytological and molecular comparisons with Flabelliforma magnivora, a parasite infecting the same tissues in the same host species, reveal that these two species are very closely related, yet distinct. Moreover, both cytological and molecular data indicate that these species are quite distant from F. montana, the type species of the genus Flabelliforma. We therefore propose that F. magnivora also be placed in Hamiltosporidium gen. no

Biodesalination of saline aquaculture wastewater with simultaneous nutrient removal and biomass production using the microalgae Arthrospira and Dunaliella in a circular economy approach

Freshwater scarcity is escalating due to factors such as climate change, droughts, increased demand, population growth, and poor water management practices. A promising sustainable solution to this challenge is biodesalination using microalgae. We demonstrate that Arthrospira platensis and Dunaliella salina can thrive in saline aquaculture wastewater, reducing both its salinity and the concentration of nutrients. The salinity removal ability was quantified through measurements of electrical conductivity (EC) and ICP-OES, revealing reductions in EC by up to 45 % (from 31.5 to 17.2 ms/cm) for A. platensis and 35 % (from 31.5 to 20.5 ms/cm) for D. salina. FESEM indicated the formation of a salt layer on the surface of both microalgae, suggesting biosorption and bioaccumulation as likely mechanisms. FTIR spectroscopy analysis demonstrated the binding of functional groups within the cell wall of A. platensis and the cell membrane of D. salina with the ions present in the medium. Scaling up the cultivation of A. platensis in a photobioreactor under non-sterile conditions validated the processes' potential for industrial-scale biodesalination. Although the treated water did not reach the standards for irrigation or potable use, this approach provides a preliminary desalination step, reducing burden on subsequent treatments and simultaneously providing nutrient removal and biomass production

Potential of algae turf scrubbers (ATS™) for elimination of phosphorus from swimming ponds

Algal Turf Scrubbers (ATS) are water treatment devices that use light and nutrients in the (waste)water to grow periphyton community; undesirable chemicals are removed by physical, chemical and biological processes. So far, most ATS systems were operated in water bodies with relatively high nutrient concentrations. Little is known about the performance of ATS under low concentration of phosphorous (P), yet there are potential applications where such conditions are met. The paper presents a series of experiments that focus on the implementation of small-scale ATS systems to eliminate P from natural swimming ponds (SP). SPs are typically subject to fluctuating P concentrations and require the maintenance of very low levels of P (< 10 μg L-1) in order to prevent undesirable algal growth. ATS systems proved to be capable of maintaining such low levels, both in laboratory and field conditions

Cultivation of the PHB-producing cyanobacterium Synechococcus leopoliensis in a pilot-scale open system using nitrogen from waste streams

PHB-producing cyanobacteria may provide the raw material for bio-based and biodegradable plastics. To commercialize photoautotrophic PHB production, their cultivation needs to be scaled up in open systems and to reduce costs and increase sustainability, nutrients must be obtained from waste streams. Here, the feasibility of these steps was verified. Different PHB-producing cyanobacteria were compared in laboratory-scale cultivations using either water from recirculating aquaculture systems or pre-processed liquid digestate as nutrient sources. Then, Synechococcus leopoliensis was cultivated in an open thin-layer photobioreactor (18 m2, 200 L), were growth in mineral Z-medium was again compared to said waste streams. All cultivations were successful. Cultivation in mineral medium resulted in both the highest final biomass yield (6 g L−1) and productivity (0.7 g L−1 d−1). Both waste stream-based media showed lower biomass yields and productivities (2 g L−1 and 0.25–0.3 g L−1 d−1). However, due to differences in the cultivation conditions (e.g., temperature, nutrient supply), final biomass yield and productivity do not represent the performance of the cultivations adequately. Relative parameters such as nitrogen and energy conversion ratios indicate that cultivation with aquaculture water suffered from insufficient nitrogen supply to the culture, whereas the use pre-processed liquid digestate resulted in a substantial loss of nitrogen due to volatilization. All cultivations in the open system were continued in the laboratory, where cultures were starved for ten days under nutrient-depleted conditions (without nitrogen, phosphorus, or both). While PHB accumulation occurred, concentrations were comparatively low (< 1%dw). The comparison of the results suggests that PHB yields were influenced more by the initial cultivation condition than by the specific type of nutrient depletion. Thus, while the cultivation with waste streams in an open system is feasible, environmental parameters seem to influence PHB yields considerably and must be considered for the optimization of the complete process

Fitness benefits to bacteria of carrying prophages and prophage‐encoded antibiotic‐resistance genes peak in different environments

Understanding the role of horizontal gene transfer (HGT) in adaptation is a key challenge in evolutionary biology. In microbes, an important mechanism of HGT is prophage acquisition (phage genomes integrated into bacterial chromosomes). Prophages can influence bacterial fitness via transfer of beneficial genes (including antibiotic-resistance genes, ARGs), protection from superinfecting phages, or switching to a lytic lifecycle which releases free phages infectious to competitors. We expect these effects to depend on environmental conditions because of, for example, environment-dependent induction of the lytic lifecycle. However, it remains unclear how costs/benefits of prophages vary across environments. Here, studying prophages with/without ARGs in Escherichia coli, we disentangled effects of prophages alone and adaptive genes they carry. In competition with prophage-free strains, benefits from prophages and ARGs peaked in different environments. Prophages were most beneficial when induction of the lytic lifecycle was common, whereas ARGs were more beneficial upon antibiotic exposure and with reduced prophage induction. Acquisition of prophage-encoded ARGs by competing strains was most common when prophage induction, and therefore free phages, were common. Thus, selection on prophages and adaptive genes they carry varies independently across environments, which is important for predicting the spread of mobile/integrating genetic elements and their role in evolution

Co-cultivation of microalgae in aquaculture water : interactions, growth and nutrient removal efficiency at laboratory- and pilot-scale

- Successful co-cultivation of Chlorella vulgaris and Tetradesmus obliquus - Stable cultivation despite presence of protozoa - Shifts in species frequency in co-culture likely caused by protozoa - Pilot-scale cultivation reached a final dry weight of 11.1 g l−1 - Maximum productivity at pilot-scale was 13.3 g m−2 d−1Microalgae biotechnology is of increasing importance and a central application concerns the treatment of wastewater. Here, its implementation in a recirculating aquaculture system (RAS) to lower the discharge of wastewater is studied. To better cope with external variations in culture conditions, a co-cultivation of two species of microalgae, Chlorella vulgaris and Tetradesmus obliquus, was used to obtain a more reliable and robust culture and was compared to monocultures. This approach was tested using RAS water both under sterile and non-sterile conditions at laboratory scale and then compared to a co-culture at pilot-scale in an open thin-layer photobioreactor. Performance of cultures was tested in terms of microalgae growth and nutrient removal efficiency. Furthermore, to better understand the interaction between environmental variables and each microalgae species, their relative frequencies in co-cultures as well as the presence of protozoa and bacteria were monitored. All growth experiments were carried out successfully and, unlike in a previous study, no crashes were observed. However, shifts in species frequency in co-cultures indicated that the two species were differentially affected by cultivation conditions. Despite nutrient limitation, the pilot-scale cultivation had a high productivity (13.3 g m−2 d−1) and final dry weight (11.1 g l−1) after 29 days and demonstrated its suitability for RAS water treatment

High-density cultivation of microalgae continuously fed with unfiltered water from a recirculating aquaculture system

Water from recirculating aquaculture systems (RAS) has been shown to be a suitable growth medium for microalgae and their cultivation can, therefore, be used to reduce RAS emissions. However, while efficient wastewater treatment is possible, the nutrient content of RAS water limits attainable microalgae biomass densities to 1–2 g/l at best, which requires frequent harvesting of microalgae. We have taken advantage of the constant evaporation of water from an open thin-layer photobioreactor (200  l volume, 18  m2 illuminated surface, artificial supply of CO2) to continuously add water from RAS to a microalgae culture and thereby provide nutrients for continued growth while evaporating all water. To test for a possible inhibitory effect of RAS water on microalgae growth, components of mineral medium were omitted stepwise in subsequent cultivations and replaced by RAS water as the only source of nutrients. This approach showed that microalgae can be grown successfully for up to three weeks in RAS water without additional nutrients and that high (20  g/l) biomass densities can be attained. While growth in wastewater did not reach productivities measured in mineral medium, analysis of growth data suggested that this reduction was not due to an inhibitory effect of the RAS water but due to an insufficient supply rate of nutrients, even though RAS water contained up to 158  mg/l NO3-N. It is, therefore, concluded that this method can be used to fully treat the wastewater discharge of a RAS. Furthermore, because both water evaporation from and microalgae growth in the photobioreactor correlated positively with each other due to their shared dependency on solar radiation, supply of nutrients continuously adjusts to changes in demand. It is estimated that the area of a photobioreactor required to treat all emissions of a RAS requires approximately 6.5 times the area of the latter